Some hybrid vehicles use a primary power source for the majority of the vehicle's propulsion needs and supplement that with an auxiliary power source, as needed. For instance, a high-voltage battery and one or more electric motors may act as the primary power source for the hybrid vehicle, while an internal combustion engine may act as the auxiliary power source. Certain driving conditions, such as when the driver requests a significant amount of torque or acceleration, can present unique challenges for hybrid vehicles.
For example, when a driver aggressively engages the accelerator pedal of a hybrid vehicle, an electric motor (primary power source) may exhaust or at least diminish much of the stored charge on the battery. If the state-of-charge (SOC) of the battery falls beneath a certain threshold, the hybrid vehicle may have to rely on an internal combustion engine (auxiliary power source) to provide supplemental power for propulsion. However, starting the internal combustion engine immediately following engagement of the accelerator pedal may give the driver the false impression that the hybrid vehicle is primarily relying upon engine-based propulsion, as opposed to battery-based propulsion that is merely supplemented by the engine. Some drivers may find this undesirable. In addition, starting the internal combustion engine immediately following engagement of the accelerator pedal (i.e., when the hybrid vehicle is already under a heavy load or demand) can be rather noticeable to the driver and can negatively impact the drive quality of the vehicle, as will be explained in more detail.